Liquid collection

ABSTRACT

A liquid collection apparatus comprises a liquid collecting device and liquid conduit for transferring liquid from the liquid collection device. Porous liquid absorption device is positioned between the liquid collection device and the liquid conduit. Pump device pumps liquid from the liquid conduit, the pump device generating a pressure in the conduit that is sufficient to draw liquid through the liquid collection device but is insufficient to draw a gas/liquid surface through the liquid absorption device.

This invention relates to apparatus and method for collecting liquidsand, in particular, to liquid collection apparatus and methods of thetype employed in printing devices to collect unused ink.

Traditional liquid collection devices collect liquid (in the case ofprinting, ink) for reuse in the process in which the liquid is beingemployed. Such liquid collection devices do, however, have problemsassociated with them.

One significant problem is that air can be collected with the liquid andmixed with it by the collection device. The air can containcontaminants, which are drawn into the liquid, reducing the quality ofthe recycled liquid. A further problem, particular to printing inks, isthat mixing of the inks with air can lead to ink solvent evaporationinto the air, increasing the viscosity of the ink.

The present invention is directed towards the provision of a liquidcollection apparatus which collects liquid without collecting airtrapped therein.

According to the present invention there is provided a liquid collectionapparatus comprising:

means for collecting liquid;

liquid conduit means for transferring liquid from the liquid collectionmeans;

porous liquid absorption means positioned between the liquid collectionmeans and the liquid conduit; and

pump means for pumping liquid from the liquid conduit, the pump meansgenerating a pressure in liquid in the conduit that is sufficient todraw liquid through liquid collection means but is insufficient to drawa gas/liquid surface through the liquid absorption means.

Because the pressure generated by the pump means is not sufficient todraw a gas/liquid surface through the porous liquid absorption meansagainst surface tension forces in the absorption means, any gascontained within the liquid will not be drawn through the liquidabsorption means and into the liquid conduit.

The apparatus may be arranged to be employed in an ink jet printhead, inwhich case the liquid may be ink. The liquid absorption means may havepores of a diameter of one micron or less. The pore diameters may be inthe range of 0.2 to 1 micron. Alternatively, it may be formed from aplurality of narrow capillaries.

The material from which the liquid absorption means is formed will bedependent upon the type of liquid being collected, but may formed fromcellulose, nylon, mixed esters, or polypropylene.

The liquid collecting means may be arranged so that the surface of theliquid absorption means is not in direct contact with the atmosphere, toreduce the possibility of liquid retained by the absorption means dryingdue to contact with the atmosphere. The liquid collection means may beformed from a plurality of ribs or of an absorbent material containingpores/capillaries of larger diameter than those in the liquid absorptionmeans. Such an arrangement provides an apparatus which can be movedwithout liquid spilling out due to the effects of the motion and/orgravity.

According to the present invention there is also provided a method ofcollecting liquid, the method comprising the steps of:

collecting liquid in a liquid collection means; and

drawing the liquid through a porous liquid absorption means at apressure level which ensures liquid flow through the liquid collectionmeans yet which is insufficient to draw liquid through the liquidabsorption means.

Referring to FIGS. A & B, a liquid collection apparatus according to thepresent invention has a liquid collection means 1 in the form of agutter. A conduit 2 is connected to a pump (not shown). Positionedbetween the liquid collection means 1 and conduit 2 is a liquidabsorption means 3. This liquid absorption means 3 has, in this example,a structure such that it has a plurality of pores of a diameter of 1micron or less.

In operation, the pump is operated to draw liquid collected by theliquid collection means 1 through the liquid absorption means 3 and intothe conduit 2. The strength of the pump is such that it creates asufficient pressure differential across the liquid absorption means 3 toensure liquid flow therethrough. The operation of the pump iscontrolled, however, such that it does not generate a sufficientpressure differential to draw the gas/liquid surface through theabsorption means 3. This ensures that, if air or any gas is draw intothe liquid collection means 1 it is not drawn into the absorption means3 because the constant presence of liquid at the interface between theliquid and the gas at the boundary 4 between the collection means 1 andliquid absorption means 3 prevents the gas being drawn into the conduit2.

As mentioned above, the material from which the porous liquid absorptionmeans 3 is formed will be dependent upon the type of liquid beingcollected, and should be selected so that it does not react with thecollection liquid.

As also mentioned above, the liquid collection means may include aplurality of ribs 5 to retain the liquid in use, and prevent spillage.Alternatively, it may be formed from absorbent material (not shown) of adensity lower than that of the absorption means 3.

In this example, the arrangement shown is employed to collect ink from acontinuous ink jet printhead. It will be appreciated, however, that thecollection device of the invention has applications in many otherfields.

What is claimed is:
 1. A liquid collection apparatus comprising: aliquid collecting means; liquid conduit for transferring liquid from theliquid collection means; porous liquid absorption means positionedbetween the liquid collection means and the liquid conduit; and pumpmeans for pumping liquid from the liquid conduit, the pump meansgenerating a pressure in the conduit that is sufficient to draw liquidthrough the liquid collection means but is insufficient to draw agas/liquid surface through the liquid absorption means.
 2. An apparatusaccording to claim 1, wherein the liquid absorption means has pores of adiameter of one micron or less.
 3. An apparatus according to claim 2,wherein the pore diameters are in the range of 0.2 to 1 micron.
 4. Anapparatus according to claim 1, wherein the liquid absorption means isformed from a plurality of narrow capillaries.
 5. An apparatus accordingto claim 1, wherein the material from which the liquid absorption meansis formed is one of cellulose, nylon, mixed esters, or polypropylene. 6.An apparatus according to claim 1, wherein the liquid collection meansis formed from a plurality of ribs.
 7. An apparatus according to claim1, wherein the liquid collection means is formed from an absorbentmaterial containing pores/capillaries of larger diameter than those inthe liquid absorption means.
 8. An apparatus according to claim 1arranged to be employed in an ink jet printhead.
 9. A method ofcollecting liquid, the method comprising the steps of: collecting liquidin a liquid collection means; and drawing the liquid through a porousliquid absorption means at a pressure level which ensures liquid flowthrough the liquid collection means yet which is insufficient to draw agas/liquid surface through the liquid absorption means.